Frequency effects of alternating dielectric-barrier-discharge plasma actuation on turbulent flow of circular cylinder

Abstract An in-house solver for the three-dimensional, unsteady, compressible Navier–Stokes equations with a large-eddy simulation (LES) turbulence model is applied to simulate the unsteady flow over a circular cylinder at a Reynolds number of 15,000 under the control of a pair of symmetrically-installed dielectric-barrier-discharge (DBD) plasma actuators on its upper and lower surfaces. The two plasma actuators are operated in an antisymmetric duty-cycle mode, with the actuation frequency varying from one-quarter to five times the natural vortex-shedding frequency. The results indicate that plasma actuation generally reduces the drag coefficient relative to the uncontrolled baseline case, achieving a maximum drag reduction of 67 % at an actuation frequency five times the natural vortex-shedding frequency. However, when the actuation frequency is close to the natural vortex-shedding frequency of the baseline flow, the drag coefficient exceeds the baseline value because the plasma-induced jets are significantly strengthened and stay attached to the cylinder surface, resulting in a relatively low pressure level on the leeward surface. For the two cases with actuation frequencies equal to three and five times the natural vortex-shedding frequency, the spectral peak of the lift coefficient at the natural vortex-shedding frequency disappears and is replaced by a dominant peak at 1.5 times the natural vortex-shedding frequency.